Method for manufacturing ammonia synthesis catalyst, and method for manufacturing ammonia

ABSTRACT

Provided is a method for manufacturing a catalyst with which it is possible to obtain a supported metal ammonia synthesis catalyst, in which there are restrictions in terms of producing method and producing facility, and particularly large restrictions for industrial-scale producing, in a more simple manner and so that the obtained catalyst has a high activity. This method for manufacturing an ammonia synthesis catalyst includes: a first step for preparing 12CaO.7Al 2 O 3  having a specific surface area of 5 m 2 /g or above; a second step for supporting a ruthenium compound on the 12CaO.7Al 2 O 3 ; and a third step for performing a reduction process on the 12CaO.7Al 2 O 3  supporting the ruthenium compound, obtained in the second step. This invention is characterized in that the reduction process is performed until the average particle diameter of the ruthenium after the reduction process has increased by at least 15% in relation to the average particle diameter of the ruthenium before the reduction process.

TECHNICAL FIELD

The present invention relates to a method for manufacturing an ammoniasynthesis catalyst and a method for manufacturing ammonia.

Priority is claimed based on Japanese Patent Application No. 2016-155951filed in Japan on Aug. 8, 2016, the contents of which are herebyincorporated by reference.

BACKGROUND ART

Nitrogen fertilizers, such as ammonium sulfate and urea, widely used inagricultural production, are produced using ammonia as a main rawmaterial. Therefore, ammonia has been studied as a very importantchemical raw material and its production method has been studied.

The most widely used ammonia production technology is the Harbor-Boschmethod. The Haber-Bosch method is a method for manufacturing ammonia,and the method includes contacting nitrogen and hydrogen as a rawmaterial with a catalyst containing iron as a main component at hightemperature and high pressure.

As a synthesis method other than the Harbor-Bosch method, a synthesismethod using a metal-supported catalyst in which a metal such as Ru, Co,Fe or the like is supported on various supports has been studied.

On the other hand, there is a compound called “mayenite-type compound”,which is a calcium aluminosilicate containing CaO, Al₂O₃, and SiO₂. Thecompound has the same type of crystal structure as that of mayenite. Therepresentative composition of the mayenite-type compound is representedby 12CaO.7Al₂O₃.

The mayenite-type compound has the following structure (Non-PatentDocument 1). In a unit cell containing two molecular formulae, there are66 oxide ions. Among the 66 oxide ions, two oxide ions are included as“free oxide ions” in a space inside a cage formed by the crystalskeleton.

The present inventors found that the free oxide ions in themayenite-type compound can be substituted with various anions.Particularly, when the mayenite-type compound is held at a hightemperature under a strong reduction atmosphere, it is possible toreplace all the free oxide ions with electrons. The mayenite-typecompound in which the free oxide ions are substituted with electrons isa conductive mayenite-type compound having a good electronicconductivity (Non-Patent Document 2.). In addition, the mayenite-typecompound in which the free oxide ions are substituted with electrons issometimes referred to as “C12A7 electride”.

The present inventors found that the catalyst using the C12A7 electridecan be used as an ammonia synthesis catalyst (Patent Document 1).Specifically, an ammonia can be synthesized by contacting a nitrogen anda hydrogen with a supported metal catalyst, in which a transition metalsuch as Ru, Fe, Co or the like is supported on the C12A7 electride as acatalytic support. The supported metal catalyst has a higher activityfor synthesizing ammonia and a higher performance in synthesizingammonia than the conventional supported metal ammonia synthesiscatalyst.

The C12A7 electride can be obtained by heating a mayenite-type compoundin a reduction atmosphere. The catalyst using the C12A7 electride can beobtained by supporting a transition metal compound to be a catalyticallyactive component onto the C12A7 electride and then subjecting it toreduction process. A method for manufacturing the conductivemayenite-type compound has also been studied (Patent Document 2). As amethod of improving its specific surface area, a mayenite-type compoundhaving fine pores has been proposed.

-   [Patent Document 1] International Publication WO2012/077658-   [Patent Document 2] International Publication WO2014/034473-   [Non-Patent Document 1] H B Bartl, T. Scheller and N. Jarhrb,    Mineral Monatch. 1970, 547.-   [Non-Patent Document 2] S. Matuishi, Y. Toda, M. Miyakawa, K.    Hayashi, T. Kamiya, M. Hirano, I. Tanaka and H. Hosono, Science 301,    626-629 (2003).

SUMMARY OF INVENTION

The C12A7 electride is usually produced by injecting electrons into themayenite-type compound. The step of injecting electrons into themayenite-type compound usually requires heating at a high temperatureand under a reduction atmosphere and requires handling in a sealedcontainer or an atmosphere of an inert gas (Ar or the like). Therefore,the reaction operation becomes complicated. Particularly when themanufacturing scale becomes large, a dedicated manufacturing apparatusis required. There is concern that load of manufacturing facilities andmanufacturing cost will increase.

On the other hand, injecting electrons into the mayenite-type compoundrequires a heat process at high temperature. Therefore, even amayenite-type compound having micro-pores and having a large specificsurface area is used, the micro-pores are destroyed when it is exposedto a high temperature condition. As a result, there is a problem thatfurther improvement in performance cannot be achieved because thespecific surface area of the C12A7 electride is lowered duringproduction of the catalyst.

In the production of the supported metal catalyst using the C12A7electride as a catalytic support, there are problems in terms ofmanufacturing methods and manufacturing facilities, in a case of tryingto improve the performance of the catalyst, and especially in a case ofconsidering manufacturing on an industrial scale. Therefore, there is ademand for a method that can produce a catalyst with a higher activityby using a more convenient method.

The present inventors conducted intensive studies to solve theabove-mentioned problems, and as a result, they found that when amayenite-type compound in which no electron is injected is used as acatalytic support, a catalyst for synthesis of ammonia having anefficient reaction activity can be obtained by a simpler productionmethod by undergoing a certain treatment condition.

That is, the gists of the present invention are as follows.

[1] A method for manufacturing an ammonia synthesis catalyst, the methodcomprising: a first step of preparing 12CaO.7Al₂O₃ having a specificsurface area of 5 m²/g or more; a second step of supporting a rutheniumcompound on the 12CaO.7Al₂O₃; and a third step of performing reductionprocess on the 12CaO.7Al₂O₃ on which the ruthenium compound is supported(hereinafter referred to as ruthenium-supported C12A7) obtained in thesecond step, wherein the reduction process is carried out until anaverage particle diameter of a ruthenium after the reduction processincreases by 15% or more with respect to an average particle diameter ofa ruthenium before the reduction process.

[2] The method for manufacturing an ammonia synthesis catalyst accordingto [1], wherein the specific surface area of the ruthenium-supportedC12A7 after the reduction process step is 5 m²/g or more.

[3] The method for manufacturing an ammonia synthesis catalyst accordingto [1] or [2], wherein in the first step, preparing 12CaO.7Al₂O₃ iscarried out by a hydrothermal synthesis method, a sol-gel method, acombustion synthesis method or a co-precipitation method.

[4] The method for manufacturing an ammonia synthesis catalyst accordingto any one of [1] to [3], wherein in the second step, supporting theruthenium compound is carried out by an impregnation method or a vapordeposition method.

[5] The method for manufacturing an ammonia synthesis catalyst accordingto any one of [1] to [4], wherein in the step of performing reductionprocess, the reduction process is carried out by using a gas containinghydrogen.

[6] The method for manufacturing an ammonia synthesis catalyst accordingto any one of [1] to [5], the method further comprises, following thefirst step, a step of molding the 12CaO.7Al₂O₃ obtained in the firststep,

[7] The method for manufacturing an ammonia synthesis catalyst accordingto any one of [1] to [5], the method further comprises, following thesecond step, a step of molding the ruthenium-supported C12A7 obtained inthe second step

[8] The method for manufacturing an ammonia synthesis catalyst accordingto any one of [1] to [7], wherein the ammonia synthesis catalystcomprises at least an alkali metal atom or an alkaline earth metal atom.

[9] A method for manufacturing ammonia, comprising: a first step ofpreparing 12CaO.7Al₂O₃ having a specific surface area of 5 m²/g or more;a second step of supporting the ruthenium compound on the 12CaO.7Al₂O₃;a third step of performing reduction process on the 12CaO.7Al₂O₃ onwhich a ruthenium compound is supported (hereinafter referred to asruthenium-supported C12A7) obtained in the second step, wherein thereduction process is carried out until an average particle diameter of aruthenium after the reduction process increases by 15% or more withrespect to the average particle diameter of a ruthenium before thereduction process; and a step of producing ammonia by contacting a gascontaining nitrogen and hydrogen with the ammonia synthesis catalystwhich is obtained by the reduction process in the third step.

[10] The method according to [9], wherein in the reduction process step,the reduction process is performed by using a gas containing hydrogen.

[11] The method according to claim [9], wherein in the reduction processstep, the reduction process is performed with a gas containing hydrogenand nitrogen.

[12] The method according to any one of claims [9] to [11], wherein theammonia synthesis catalyst comprises at least an alkali metal atom or analkaline earth metal atom.

[13] A metal-supported material, comprising 12CaO.7Al₂O₃; and pluralkinds of metal atoms supported on the 12CaO.7Al₂O₃, wherein a specificsurface area of the 12CaO.7Al₂O₃ is 5 m²/g or more; and the plural kindsof metal atoms comprises a metal ruthenium, and an alkali metal atom oran alkaline earth metal atom.

[14] The metal-supported material according to [13], wherein the alkalimetal atom or the alkaline earth metal atom is an oxide of an alkalimetal or an oxide of an alkaline earth metal.

[15] The metal-supported material according to [13] or [14], wherein thealkali metal atom or the alkaline earth metal atom is barium.

[16] A catalyst comprising the metal-supported material according to anyone of claims [13] to [15].

[17] The catalyst according to claim 16, wherein the catalyst is usedfor ammonia synthesis.

[18] A method for manufacturing ammonia, the method comprising:

contacting a gas containing nitrogen and hydrogen with the catalystaccording to claim [16] or [17].

By using the method for manufacturing a catalyst of the presentinvention, a catalyst having higher performance as an ammonia synthesiscatalyst can be easily produced, than a catalyst using a conventionalC12A7 electride as a catalytic support. In particular, an ammoniasynthesis catalyst can be provided by a production method suitable forindustrial production.

By using the method for manufacturing the catalyst of the presentinvention, a catalyst can be produced, wherein when the catalyst is usedas an ammonia synthesis catalyst, ammonia is stably produced even if thereaction is continued for a long time, and decrease in reaction activityis small. That is, since the lifetime of the obtained catalyst is long,it is advantageous in that ammonia can be produced with a highproduction efficiency.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing results of reactions for ammonia synthesisusing the ammonia synthesis catalysts described in Examples 1 to 3.

FIG. 2 is a graph showing an investigation result (Example 3A) of achange in pressure of an ammonia synthesis reaction when the ammoniasynthesis catalyst described in Example 3 was used.

FIG. 3 is a graph showing the results of ammonia synthesis reactionsusing the ammonia synthesis catalysts described in Example 4 andComparative Example 4.

FIG. 4 is a graph showing the results of ammonia synthesis reactionsusing the ammonia synthesis catalysts described in Example 2 and Example5.

FIG. 5 is a graph showing a time change of an ammonia synthesis reactionwhen the metal-supported material described in Example 6 was used as anammonia synthesis catalyst.

FIG. 6 is a graph showing an investigation result (Example 11) of achange in pressure of an ammonia synthesis reaction when themetal-supported material described in Example 6 was used as an ammoniasynthesis catalyst.

FIG. 7 is a graph showing a result (Example 12) of a change intemperature of an ammonia synthesis reaction when the metal-supportedmaterials described in Example 6 and Example 2 were used as an ammoniasynthesis catalyst.

DESCRIPTION OF EMBODIMENTS

A first aspect of the present invention is related to a method formanufacturing an ammonia synthesis catalyst, and the method includesprescribed producing steps described later by using 12CaO.7Al₂O₃ havinga large specific surface area.

A second aspect of the present invention is related a metal-supportedmaterial having a plural kinds of metal atoms supported on 12CaO.7Al₂O₃having a specific surface area of 5 m²/g or more, wherein the metalatoms are a metal ruthenium, and an alkali metal atom or an alkali. Thesecond aspect of the present invention is also related to an ammoniasynthesis catalyst using the metal-supported material.

Hereinafter, the present invention will be described in detail.

<Mayenite-Type Compound>

The mayenite-type compound is a calcium aluminosilicate containing CaO,Al₂O₃ and SiO₂ and has a crystal structure of the same type as mayenite.The representative composition of the mayenite-type compound isrepresented by 12CaO.7Al₂O₃.

The crystals of mayenite-type compounds are composed of cage-likestructures (cages) which wall surfaces are shared and which areconnected three-dimensionally. Usually anions such as O²⁻ are containedinside the cage of the mayenite-type compound, however, the anions canbe replaced with conduction electrons by chemical treatment.

The mayenite-type compound used in the present invention is hereinafterreferred to as 12CaO.7Al₂O₃ and sometimes abbreviated simply as “C12A7”.

The specific surface area of 12CaO.7Al₂O₃ used in the present inventionis 5 m²/g or more. By using the 12CaO.7Al₂O₃ having a specific surfacearea not less than the above range, a high catalytic activity can beobtained when it is used as an ammonia synthesis catalyst. Below theabove range, a sufficient catalytic activity cannot be obtained. Thespecific surface area is preferably 10 m²/g or more, and more preferably15 m²/g or more. Although the upper limit is not particularly limited,it is preferably 200 m²/g or less, more preferably 100 m²/g or less.Within the above range, it is advantageous in respect of handleabilityof powder of the catalyst or in respect of moldability.

The shape of 12CaO.7Al₂O₃ used in the present invention is notparticularly limited. Usually, fine particles, granular particles, bulkform and the like can be used. It is preferably to use fine particles orbulk form, more preferably to uses fine particles. When themayenite-type compound is made into fine particles, the surface area permass increases. The gap between the particles is not particularlylimited, but is preferably within a mesoporous region of 2 nm or moreand 100 nm or less.

In the case of bulk form, although not particularly limited, it ispreferable that it is a porous body having a pore structure. By having apore structure, it is possible to obtain 12CaO.7Al₂O₃ having a higherspecific surface area.

When the shape of 12CaO.7Al₂O₃ is fine particles, its particle diameteris not particularly limited. The primary particle size is 5 nm or more,preferably 10 nm or more; and 500 nm or less, preferably 100 nm or less.

The ammonia synthesis catalyst obtained by the present invention can beobtained by supporting a catalytically active metal on a mayenite-typecompound.

Ruthenium (Ru) is used as a catalytically active metal in the ammoniasynthesis catalyst in the present invention. Ruthenium may be used aloneor in combination with a metal element other than ruthenium.

The metal element other than ruthenium is not particularly limited aslong as it does not inhibit an activity of the ammonia synthesiscatalyst obtained in the present invention. It is preferable to use oneor more transition metals selected from Group 3, Group 8, Group 9 orGroup 10 of the periodic table, more preferably yttrium, iron or cobalt.

It is preferable to use Ru alone, from the viewpoint of obtaining stablecatalytic activity. Compared with the case where two or more kinds ofcatalytically active metals are used, in the case where Ru alone isused, a surface composition of the catalyst is unlikely to change bychanging reduction process condition or the like. Therefore, a desiredammonia synthesis activity can be easily obtained.

The amount of Ru is not particularly limited. With respect to the massof the catalytic support C12A7, the amount of Ru is 0.01% by mass ormore, preferably 0.02% by mass or more, more preferably 0.05% by mass ormore; and the amount of Ru is 30 mass % or less, preferably 20 mass % orless, more preferably 10 mass % or less. Within the above range, theobtained catalyst can have sufficient active points, an efficientcatalyst can be obtained, and a catalyst favorable in terms of cost canbe obtained.

The ammonia synthesis catalyst obtained by the present invention maycontain components other than the mayenite-type compound and thecatalytically active metal as long as they do not disturb the object ofthe present invention.

For example, a component serving as a binder (binder) component forfacilitating the molding of the catalyst can be added.

Specific examples thereof include metal oxides such as SiO₂, Al₂O₃,ZrO₂, TiO₂, La₂O₃, CeO₂, and Nb₂O₅; and carbon materials such asactivated carbon, graphite and SiC.

The ammonia synthesis catalyst obtained by the present invention maycontain an alkali metal atom or an alkaline earth metal atom as acomponent thereof. Since these components can function as reactionaccelerators in the synthesis of ammonia when these components arepresent in the catalyst, it is preferable to contain these components.

The type of the alkali metal atom is not particularly limited, forexample, lithium, sodium, potassium, cesium, rubidium or the like can beused.

The type of alkaline earth metal atom is not particularly limited, forexample, magnesium, strontium, barium or the like can be used.

Among the above-mentioned metal atoms, a barium atom is preferable.

The form of alkali metal atoms and alkaline earth metal atoms is notparticularly limited. Examples include hydroxides of each atom;inorganic acid salts such as carbonates and nitrates; carboxylates suchas acetates and formates; alkoxides such as ethoxide; and other organiccompounds containing each atom. The addition amount of the reactionaccelerators is not particularly limited. The addition amount of thereaction accelerators is 0.01 times or more; and 50 times or less,preferably 20 times or less in terms of a molar ratio of each metal withrespect to ruthenium atoms contained in the catalyst.

The adding method is not particularly limited as long as the metal atomof alkali metal atoms and alkaline earth metal atoms, which may be usedas reaction accelerators, may be present in the reaction field duringthe ammonia synthesis reaction. Examples of a method of adding the metalmay include a method of mixing the metal when preparing themayenite-type compound in the first step to be described later andproducing a mayenite-type compound containing them; a method ofco-supporting the metal atom when supporting a Ru metal source in asecond step to be described later; a method of adding the metal atomwhen molding the catalyst; and the like.

<Method for Manufacturing Ammonia Synthesis Catalyst>

The method for manufacturing an ammonia synthesis catalyst according tothe first aspect of the present invention (hereinafter, the productionmethod of the present invention) includes the following first step tothird step, which will be described in this order.

<First Step: Preparing Mayenite-Type Compound (12CaO.7Al₂O₃)>

The production method of the present invention includes a step ofpreparing 12CaO.7Al₂O₃ having a specific surface area of 5 m²/g or moreas a first step.

The raw material for producing 12CaO.7Al₂O₃ having a specific surfacearea of 5 m²/g or more is not particularly limited. Depending on theproduction method, various calcium-containing materials (hereinafterreferred to as calcium atom sources) and aluminum-containing materials(hereinafter referred to as aluminum atom sources) may be used.

Specific examples of the calcium atom source include calcium hydroxide;calcium oxide; calcium salt such as calcium nitrate, calcium chloride,and calcium acetate; calcium alkoxide such as calcium ethoxide, calciumpropoxide, calcium isopropoxide, calcium butoxide, calcium isobutoxide;and the like.

Specific examples of the aluminum atom source include aluminumhydroxide; aluminum oxide; aluminum salts such as aluminum nitrate,aluminum chloride and aluminum acetate; aluminum alkoxide such asaluminum ethoxide, aluminum propoxide, aluminum isopropoxide, aluminumbutoxide and aluminum isobutoxide; aluminum acetylacetonate; and thelike.

The mayenite-type compound (12CaO.7Al₂O₃) may contain an atom other thanCa, Al and oxygen as long as it does not disturb the object of thepresent invention.

Specifically, the first step of the present invention can be carried outby using an alkali metal atom or an alkaline earth metal atom used as areaction accelerator together with the calcium atom source and thealuminum atom source.

“Containing atoms other than Ca, Al, and oxygen” means that themayenite-type compound (12CaO.7Al₂O₃) contains a substance having atomsother than Ca, Al, and oxygen as constituent components. Specifically,for example, “containing an alkaline earth metal atom” means containinga simple substance of an alkaline earth metal, a salt of an alkalineearth metal, an oxide of an alkaline earth metal, a hydroxide of analkaline earth metal, or the like.

A method of preparing 12CaO.7Al₂O₃ having a specific surface area of 5m²/g or more is not particularly limited. For example, a hydrothermalsynthesis method, a sol-gel method, a combustion synthesis method, or aco-precipitation method can be used. The hydrothermal synthesis methodis preferable from the viewpoint that it is simple and capable ofobtaining 12CaO.7Al₂O₃ having a high surface area with goodreproducibility.

<Hydrothermal Synthesis Method>

The hydrothermal synthesis method has been studied for a long time as amethod of synthesizing fine inorganic oxide particles having goodcrystallinity. In particular, the method includes, firstly, obtaining aprecursor compound of the inorganic oxide by placing a solvent such aswater or alcohol and a raw material of an inorganic oxide in a pressureresistant container, and then heating them at a temperature equal to orhigher than the boiling point of the solvent for several hours toseveral days; and subsequently, obtaining an inorganic oxide by furtherheating the resultant precursor compound.

When using a hydrothermal synthesis method, the mayenite-type compound(12CaO.7Al₂O₃) is produced by producing a hydroxide of Ca₃Al₂(OH)₁₂ as aprecursor, and then heating it in a pressure vessel at a temperatureequal to or higher than the boiling point of water.

The calcium atom source used in the hydrothermal synthesis method is notparticularly limited. Among the above calcium atom sources, calciumhydroxide, calcium oxide, or calcium salt may be used, and preferablycalcium hydroxide is used.

The aluminum atom source is not particularly limited. Among the abovecalcium atom sources, aluminum hydroxide, aluminum oxide, or aluminumsalt may be used, and aluminum hydroxide is preferably used.

A mixing ratio of the raw materials of the precursors is notparticularly limited. The mixing ratio can be appropriately adjustedaccording to the desired composition. The mixing ratio may be adjustedby a stoichiometric composition of targeted mayenite-type compound(12CaO.7Al₂O₃).

The heating temperature is not particularly limited, and the heatingtemperature can be appropriately selected as long as a sufficient yieldcan be obtained. For example, the heating temperature is 100° C. ormore, preferably 150° C. or more; and 200° C. or less. Within theabove-mentioned range, it is possible to carrying out the production byusing a commonly-used reaction apparatus, which is advantageous from theviewpoint of apparatus.

The heating time is not particularly limited, and a heating time can beappropriately selected as long as a sufficient yield can be obtained.For example, the heating time is 2 hours or more, preferably 6 hours ormore; and 100 hours or less. Within the above range, it is possible tosufficiently obtain the targeted mayenite-type compound.

12CaO.7Al₂O₃ having a specific surface area of 5 m²/g or more can beobtained by heating and dehydrating Ca₃Al₂(OH)₁₂ which is theabove-obtained precursor of the mayenite-type compound.

The heating condition is not particularly limited, and it can beappropriately selected within a range where C12A7 having a largespecific surface area can be obtained. For example, as a heatingcondition, heating in the air may be used.

The heating temperature is not particularly limited, but it can beheated at 400° C. or more, preferably 450° C. or more; and 1000° C. orless.

<Sol-Gel Method>

The mayenite-type compound (12CaO.7Al₂O₃) can be produced by a sol-gelmethod. The sol-gel method includes forming a sol by hydrolyzing anorganic compound or an inorganic compound of a metal which is a rawmaterial of a desired metal oxide in a solution; then converting the solto gel by carrying out poly-condensation; and treating the gel at hightemperature to obtain a metal oxide. The production method can becarried out according to a known method described in, for example, J.Phys. D: Appl. Phys., 41, 035404 (2008) or the like.

The method for manufacturing a catalyst of the present invention,specifically, includes dissolving an aluminum atom source as a rawmaterial in a solvent; preparing a hydrolyzed sol by adding acid afterheating and stirring the mixture; next, dissolving the calcium atomsource in a solvent; adjusting pH as necessary; forming a gel bystirring, heating and mixing the resulted solution containing thecalcium atom source with the sol containing the aluminum atom source;dehydrating and calcining it after filtering the resulting gel to obtainthe mayenite-type compound.

The calcium atom source used in the sol-gel method is not particularlylimited, and for example, a calcium hydroxide, a calcium oxide, acalcium salt or the like may be used. The calcium salt is preferable. Asthe calcium salt, a calcium nitrate is preferable.

As the aluminum atom source, although not particularly limited, aluminumhydroxide, aluminum oxide, aluminum alkoxide or the like may be used.Aluminum alkoxide is preferable.

<Combustion Synthesis Method>

As a method for manufacturing the mayenite-type compound, it is alsopossible to use a combustion synthesis method. As a specific productionmethod, the method described in J. Am. Ceram. Soc., 81, 2853-2863 (1998)may be used. For example, a mayenite-type compound can be obtained byproducing an amorphous precursor of a mayenite-type compound bydissolving a calcium atom source and an aluminum atom source in water,and heating and burning the mixed solution; and then, further heatingand dehydrating the amorphous precursor.

The calcium atom source and the aluminum atom source used in thecombustion synthesis method are not particularly limited. For example,calcium salt and aluminum salt are preferable, and calcium nitrate andaluminum nitrate are more preferable.

Specifically, for example, Ca(NO₃)₂.4H₂O and Al(NO₃)₃.9H₂O can be usedas raw materials. The raw materials may be dissolved in water instoichiometric composition, although not particularly limited. Urea isfurther added to the solution in which the raw material is dissolved,and the mixed solution is heated and burned to obtain an amorphousprecursor of the mayenite-type compound.

The heating temperature is not particularly limited. For example, theheating temperature may be 500° C. or higher.

The obtained amorphous precursor may be heated, not particularlylimited, for example, at a temperature of 700° C. or more and 1000° C.or less and dehydrated to obtain a mayenite-type compound powder C12A7.

<Co-Precipitation Method>

A co-precipitation method is a method of simultaneously precipitatinghardly-soluble salts of plural kinds of metals by using a solutioncontaining two or more kinds of metal ions. The co-precipitation methodcan prepare a highly uniform powder.

The raw material used for the co-precipitation method is notparticularly limited. Calcium salt may be used as the calcium atomsource, and calcium nitrate is preferable. Aluminum salt may be used asthe aluminum atom source, and aluminum nitrate is preferable.

Specifically, 12CaO.7Al₂O₃ can be obtained by adding an alkali such asammonia or sodium hydroxide to an aqueous solution containing calciumnitrate and aluminum nitrate; simultaneously precipitating ahardly-soluble salt containing calcium hydroxide and aluminum hydroxide;and then filtering, drying and calcining the precipitation.

<Second Step: Supporting Ruthenium Compound>

The production method of the present invention includes, as a secondstep, a step of supporting a ruthenium compound on the 12CaO.7Al₂O₃obtained in the first step.

The ruthenium compound is not particularly limited as long as it can beconverted to a metal ruthenium to be an active ingredient of an ammoniasynthesizing catalyst by a subsequent reduction process. For example, aruthenium salt, a ruthenium complex, or the like may be used.

Examples of the ruthenium salt include ruthenium chloride (RuCl₃),ruthenium chloride hydrate (RuCl₃.nH₂O), ruthenium acetate(Ru(CH₃CO₂)x), ruthenium iodide hydrate (RuI₃.nH₂O), rutheniumnitrosylnitrate (Ru(NO)(NO₃)₃), nitrosyl ruthenium chloride hydrate(Ru(NO)Cl₃.nH₂O), ruthenium trinitrate (Ru(NO₃)₃), hexaammine rutheniumchloride (Ru(NH₃)₆Cl₃), and the like. As a ruthenium salt, rutheniumchloride is preferable from the viewpoint of obtaining high ammoniasynthesizing activity without destroying the 12CaO.7Al₂O₃ structure inthe step of supporting Ru.

As the ruthenium complex, triruthenium dodecacarbonyl (Ru₃(CO)₁₂),dichlorotetrakis (triphenylphosphine) ruthenium (II) RuCl₂(PPh₃)₄),dichlorotris (triphenylphosphine) ruthenium (II) (RuCl₂(PPh₃)₃), tris(acetylacetonato) ruthenium (III) (Ru(acac)₃), ruthenocene (Ru(C₅H₅)),dichloro (benzene) ruthenium (II) dimer ([RuCl₂(C₅H₅)]₂), dichloro(mesitylene) ruthenium (II) dimer ([RuCl₂(mesitylene)]₂), dichloro(p-cymene) ruthenium (II) dimer ([RuCl₂(p-cymene)]₂) carbonylchlorohydrido tris (triphenylphosphine) ruthenium (II)([RuHCl(CO)(PPh₃)₃]), tris (dipivaloylmethanato) ruthenium (III)([Ru(dpm)₃]), or the like can be used.

As a ruthenium complex, from the viewpoint of obtaining high ammoniasynthesizing activity, triruthenium dodecacarbonyl (Ru₃(CO)₁₂), tris(acetylacetonato) ruthenium (III) (Ru(acac)₃), or ruthenocene (Ru(C₅H₅))are preferable.

Among the above ruthenium compounds, ruthenium chloride and tris(acetylacetonato) ruthenium (III) are preferable in consideration ofsafety in catalyst production and catalyst production cost.

Ru₃(CO)₁₂ may be used because ruthenium can be supported on C12A7uniformly. However, such metal carbonyl compounds may decompose at 150°C. and generate toxic CO. Therefore, it is preferable to use tris(acetylacetonato) ruthenium (III) (Ru(acac)₃), ruthenocene (Ru(C₅H₅)),or ruthenium salt because it is advantageous in that it is easy toprepare those compounds and there is no fear of safety and hygiene.

Since these compounds are easily pyrolyzed, Ru can be supported bysupporting those compounds on a catalytic support C12A7 and thenprecipitating the supported ruthenium compound in a metal state on acatalytic support after subjecting to heat treatment. In addition, Rumetal can be formed on the catalytic support by readily performingreduction process on the ruthenium compound with hydrogen gas underheating.

In the second step, a metal compound other than the ruthenium compoundcan be supported together with the ruthenium compound, wherein the metalcompound is used together with the ruthenium which is used in theammonia synthesis catalyst. As the metal compound other than theruthenium compound, it is not particularly limited as long as it doesnot inhibit supporting the ruthenium compound. For example, one or moretransition metal compounds selected from Group 3, Group 8, Group 9, orGroup 10 of the periodic table are preferable, and yttrium, iron or acobalt compound is more preferable. As the metal compound other than theruthenium compound, metal salts or metal complexes of the correspondingmetal species can be used. Examples of a metal salt of iron and cobaltinclude iron chloride (FeCl₂, FeCl₃), cobalt chloride (CoCl₃), ironacetate (Fe(CH₃CO₂)₂), iron nitrate nonahydrate (Fe(NO₃)₃.9H₂O), ironoxalate hydrate (Fe(C₂O₄).nH₂O), iron sulfate hydrate (FeSO₄.nH₂O),cobalt acetate (Co(CH₃CO₂)₂), cobalt nitrate hexahydrate(Co(NO₃)₂.6H₂O), cobalt oxalate dihydrate (Co(C₂O₄.2H₂O), cobalt sulfatehydrate (CoSO₄.nH₂O) and the like. Examples of a metal complex includepentacarbonyl iron (Fe(CO)₅), nonacarbonyl iron (Fe₂(CO)₉),tetracarbonyl iron iodide (Fe(CO)₄I₂), ferrocene (Fe(C₅H₅)₂), tris(acetylacetonato) iron (III) (Fe(acac)₃), dodecacarbonyl triiron(Fe₃(CO)₁₂), tris (acetylacetonato) cobalt (III) (Co(acac)₃), cobalt(II) acetylacetonato (Co(acac)₂), cobalt octacarbonyl (Co₂(CO)₈),cobaltocene (Co(C₅H₅)₂) and the like. Since these co-supported metalcompounds other than the ruthenium compound are easy to be thermallydecomposed, a metal other than ruthenium can be co-supported withruthenium by supporting these compounds on a catalytic support andcarrying out heat treatment to precipitate a simple transition metal onthe substrate.

It is also possible to co-support alkali metal atoms or alkaline earthmetal atoms used as the reaction accelerator.

The phrase “co-support an alkali metal atom or an alkaline earth metalatom” means that a substance having alkali metal atom or alkaline earthmetal atom as a constituent component is supported with a rutheniumcompound, wherein the substance may include a simple substance of analkali metal atom or an alkaline earth metal atom; a metal compound suchas a salt, an oxide, or a hydroxide of metal an alkali metal atom or analkaline earth metal atom; and the like.

The substance to be co-supported is not particularly limited. A simplesubstance of a metal or an oxide of a metal is preferable, and an oxideof metal is more preferable from the viewpoint of high stability when itis used in a catalytic reaction.

As a kind of the co-supported atoms, alkaline earth metal atoms arepreferable. Specifically, Sr and Ba are more preferable, and Ba is mostpreferable in that it is an element more abundantly present.

As a specific co-supported material, an oxide of an alkaline earth metalis preferable. An oxide of Ba is more preferable because Ba is not aconstituent of the support C12A7 and is an oxide of an element moreabundantly present.

Since an oxide of an alkaline earth metal which is supported on C12A7 isnot reduced to a metal even after reduction process to be describedlater, the oxide of an alkaline earth metal exists on the surface ofC12A7 together with the metal ruthenium after reduction process.

As the raw materials used for the above-mentioned co-supportingmaterials, it is not particularly limited as long as co-supported metalatoms can be supported. Examples of the raw materials includehydroxides; inorganic acid salts such as carbonates and nitrates;carboxylates such as acetates and formates; alkoxides such as ethoxide;an organic compound containing other atoms; metal complexes such asmetal acetylacetonate complexes; and the like. Among them, alkoxides,metal acetylacetonate complexes, carboxylic acid salts are preferable,and alkoxides are more preferable from the viewpoint that it is easy tocarry out a reaction.

The method of co-supporting the above-mentioned co-supported material isnot particularly limited, and an order of supporting is also notlimited. Specifically, it may be supported simultaneously with theruthenium compound or may be carried individually. Preferably, it ispreferable to support the co-supported material after supporting theruthenium compound from the viewpoint that the co-supported material canbe supported in the vicinity of the ruthenium.

The method of supporting the ruthenium compound is not particularlylimited. Examples of the methods include impregnation method, thermaldecomposition method, liquid phase method, sputtering method, vapordeposition method, and the like. In the method of supporting Ru on the12CaO.7Al₂O₃ powder, a method of carrying out molding after supporting aruthenium compound by any one of the above supporting methods ispractically used. On the other hand, in the method of supporting Ru onthe molded 12CaO.7Al₂O₃ support, the impregnation method or the vapordeposition method is preferable in that Ru can be uniformly dispersed ona single substance. The impregnation method is more preferable in thatuniform ruthenium particles can be easily formed. Specifically, in theimpregnation method, firstly, 12CaO.7Al₂O₃ is dispersed in a solutioncontaining a ruthenium compound. Subsequently, the solvent of thesolution containing 12CaO.7Al₂O₃ and the ruthenium compound wasevaporated to dryness. And then, as a result, 12CaO.7Al₂O₃ on which aruthenium compound is supported (hereinafter, may be referred to as aruthenium-supported C12A7) was obtained.

In addition, specifically, a ruthenium-supported C12A7 is obtained byphysically mixing 12CaO.7Al₂O₃ with a ruthenium compound, heating it ina vacuum atmosphere, and then depositing ruthenium on 12CaO.7Al₂O₃ bythermally decomposing the ruthenium compound.

<Third Step: Reduction Process Step>

The production method of the present invention includes a third step ofperforming reduction process on the ruthenium-supported C12A7 obtainedin the second step. In particular, the third step includes performingreduction process on the ruthenium compound supported on theruthenium-supported C12A7 to metallic ruthenium to obtain aruthenium-supported catalyst.

The reduction process in the third step of the present invention iscarried out until an average particle diameter of the ruthenium afterthe reduction process increases by 15% or more with respect to theaverage particle diameter before the reduction process. The upper limitis not particularly limited but it is not more than 200%. By performingthe reduction process within the above range, the ruthenium-supportedC12A7 can be used as a highly active ammonia synthesis catalyst.

Here, in principle, the average particle diameter of ruthenium is theaverage particle diameter obtained by the chemical adsorption methoddescribed later. When it is difficult to measure by the chemicaladsorption method, the average particle diameter means an averageparticle diameter by a direct observation method such as TEM to bedescribed later.

The average particle diameters of the ruthenium before the reductionprocess and after the reduction process are determined as the rutheniumatoms present on the surface to be measured are all metallic ruthenium.A ruthenium compound which is a ruthenium atom source may be containedas long as it does not disturb the object of the present invention.

When most of the ruthenium sources are ruthenium compounds, since theparticle diameters of ruthenium cannot be measured, the particlediameter of ruthenium may be obtained by performing reduction process atlow temperature.

The average particle diameter of ruthenium in the ruthenium-supportedcatalyst after reduction process, not particularly limited, may be 2 nmor more and 15 nm or less.

The conditions of the reduction process in the third step of the presentinvention are not particularly limited as long as they do not disturbthe object of the present invention. Examples include a method ofperforming the reduction process in an atmosphere containing a reductiongas, and a method of performing the reduction process in which areduction agent such as NaBH₄, NH₂NH₂, or formalin is added to asolution containing a Ru atom source to precipitate the metal Ru on aC12A7 surface. The method of performing the reduction process in anatmosphere containing a reduction gas is preferable. Examples of thereduction gas include hydrogen, ammonia, methanol (vapor), ethanol(vapor), methane, ethane and the like.

Further, at the time of the reduction process, components other than thereduction gas may coexist in the reaction system. In particular, at thetime of the reduction process, in addition to the reduction gas such ashydrogen, a gas such as argon or nitrogen which does not inhibit thereaction may coexist. It is preferable to coexist with nitrogen.

When the reduction process is carried out in a gas containing hydrogen,by allowing nitrogen to coexist with hydrogen, the third step can becarried out in parallel with ammonia synthesis to be described later.

The temperature of the reduction process in the third step of thepresent invention is not particularly limited. For example, thetemperature of the reduction process is 200° C. or more, preferably 300°C. or more; and 1000° C. or less, preferably 600° C. or less. Within theabove temperature range, the growth of the ruthenium particles occurssufficiently by carrying out reduction process within a preferablerange. In addition, by performing the reduction process, in an ammoniasynthesis reaction, both the activation energy and the dependence of thereaction rate on the partial pressure of hydrogen and nitrogen arealmost the same as those of the high active Ru/C12A7 electride. In thepresent invention, the pressure of the reduction process is notparticularly limited. For example, the pressure of the reduction processis 0.01 MPa or more, and 10 MPa or less. When the pressure during thereduction process is set to the same condition as the ammonia synthesiscondition described later, complicated operations are unnecessary, whichis advantageous in terms of production efficiency.

In the present invention, the time of the reduction process is notparticularly limited. When the reduction process is carried out atnormal pressure, the time of the reduction process is 20 hours or more,preferably 25 hours or more. When the reaction pressure is high, forexample, 1 MPa or more, the time of the reduction process is preferably5 hours or more.

The substance in which ruthenium is supported on C12A7, which isobtained after the reduction process, can be used as a catalyst havingammonia synthesizing activity (hereinafter sometimes simply referred toas “catalyst”).

The BET specific surface area of the catalyst obtained by the productionmethod of the present invention is not particularly limited. Forexample, the BET specific surface area is 5 m²/g or more, preferably 10m²/g or more; and 200 m²/g or less, preferably 100 m²/g or less.

The specific surface area of ruthenium-supported C12A7 obtained afterthe reduction process is about the same as that of C12A7 on which noruthenium is supported and which is used as a raw material forproduction of the ruthenium-supported C12A7.

The catalyst obtained by the production method of the present inventioncan be appropriately used as a molded body by using a conventionalmolding technique. Specific examples thereof include granular,spherical, tablet-like, ring-shaped, macaroni-like, four-leaf shaped,dice-shaped, honeycomb-shaped, and the like. The support can also beused after coating a metal-supported catalyst.

The step of molding the catalyst is carried out at any step of theproduction method of the present invention, and there is no limitation.Molding may be carried out following any one of the steps of productionmethod of the present invention.

Specifically, the production method of the present invention mayinclude, for example, after the first step, a step of molding the12CaO.7Al₂O obtained in the first step.

Further, the production method of the present invention may include,after the second step, a step of molding the ruthenium-supported C12A7obtained in the second step.

In addition, the production method of the present invention may include,after the third step, a step of molding the catalyst obtained in thethird step.

Among them, a method of including a molding step after the first step orafter the second step is preferable, in which Ru is uniformly dispersedon a support and high ammonia synthesis activity is obtained.

Further, when an alkali metal atom or an alkaline earth metal atom usedas the above-mentioned reaction accelerator, those metal atoms may beadded during molding and then the step of molding is carried out. Thosemetal atoms may also be adding to a surface of a catalyst after molding.

By using the production method according to the first aspect of thepresent invention, a metal-supported material is obtained. Themetal-supported material is a material in which plural kinds of metalatoms are supported on 12CaO.7Al₂O₃, wherein 12CaO.7Al₂O₃ has a specificsurface area of 5 m²/g or more, and the metal atoms include a metalruthenium, and an alkali metal atom or an alkaline earth metal atom.

The metal-supported material has very high activity, particularly whenused as a catalyst in an ammonia synthesis reaction. The metal-supportedmaterial is a very useful material as an ammonia synthesis catalyst.Without injecting electrons into C12A7, it is also possible to obtain acatalyst having an activity equal to or higher than that made of theC12A7 electride.

Hereinafter, the metal-supported material of the second embodiment ofthe present invention (hereinafter referred to as the metal-supportedmaterial of the present invention) and the ammonia synthesis catalystusing the same will be described.

Specifically, the metal-supported material of the present invention is ametal-supported material in which 12CaO.7Al₂O₃ having a specific surfacearea of 5 m²/g or more is used as a catalytic support, and a metalruthenium as well as an alkali metal atom or alkaline earth metal atomare supported on the catalytic support. Preferably, an alkaline earthmetal atom is supported, more preferably, a Sr or Ba atom is supported,and most preferably, a Ba atom is supported.

When an alkali metal atom or an alkaline earth metal atom is supported,although it is not particularly limited, it is preferable that oxides ofeach atom be supported from the viewpoint of high stability when used asa catalyst in the reaction.

Specifically, it is preferable that on C12A7 having a specific surfacearea of 5 m²/g or more, a metal ruthenium and an alkaline earth metaloxide are co-supported. It is more preferable that a metal ruthenium andan oxide of Ba are co-supported because Ba is not a constituent of C12A7and the oxide of Ba present abundantly on the earth.

The method for manufacturing the metal-supported material of the presentinvention is not limited as long as the effect is obtained. It ispreferable to produce it by the production method according to the firstaspect of the present invention. When the production method of thepresent invention is used, the specific production method, reactionconditions and the like are the same as described above.

The metal-supported material of the present invention can be used as acatalyst, particularly as an ammonia synthesis catalyst. The catalystcontaining the metal-supported material of the present invention or thecatalyst for synthesizing ammonia is preferable in terms of highreaction activity. Specifically, as compared with a catalysis without analkali metal atom or alkaline earth metal atom, the catalyst ispreferable because ammonia can be efficiently produced at a lowertemperature.

<Production Method of Ammonia>

The catalyst obtained by the production method of the present inventionand the catalyst containing the metal-supported material of the presentinvention can be used for ammonia synthesis reaction to produce ammonia.

Specifically, the method for manufacturing ammonia may include,following the first step to the third step in the above-mentioned methodfor manufacturing an ammonia synthesis catalyst, a fourth step ofcontacting a gas containing hydrogen and nitrogen with the obtainedcatalyst.

As a method for manufacturing ammonia, it is possible to produce ammoniaby supplying only hydrogen in the third step of the method formanufacturing the ammonia synthesis catalyst, and then, after a highlyactive catalyst is obtained, supplying nitrogen together with hydrogen.It is also possible to produce ammonia by supplying a mixed gascontaining hydrogen and nitrogen from the beginning, and thencontinuously carrying out the reduction process of the catalyst.Further, unreacted gas recovered from the reactor at this time can beused by recycling to the reactor.

The method for manufacturing ammonia of the present invention is notparticularly limited. When a gas containing hydrogen and nitrogen iscontacted with a catalyst, ammonia may be produced by heating thecatalysis.

The reaction temperature is not particularly limited. For example, thereaction temperature is 200° C. or more, preferably 250° C. or more; and600° C. or less, preferably 500° C. or less. Since ammonia synthesis isan exothermic reaction, the low temperature region is more favorable forammonia formation on a chemical equilibrium theory. However, in order toobtain a sufficient ammonia formation rate, the above temperature rangeis preferable.

A molar ratio of nitrogen and hydrogen to be contacted with the catalystis not particularly limited. For example, the molar ratio of hydrogen tonitrogen (H₂/N₂ (volume/volume)) is 1 or more and 10 or less, preferably5 or less.

A reaction pressure in carrying out the ammonia synthesis reaction ofthe present invention is not particularly limited. The reaction pressureis 0.01 MPa or more, preferably 0.1 MPa or more; and 20 MPa or less,under the pressure of a mixed gas containing nitrogen and hydrogen.

It is preferable to remove moisture and an oxide adhering to thecatalyst by using hydrogen gas or the like before supplying a mixed gascontaining nitrogen and hydrogen. As a removal method, a reductionprocess may be used. Although the catalyst is stable to moisture, inorder to obtain a better ammonia yield, not particularly limited, it ispreferable that a total moisture content in the mixed gas of nitrogenand hydrogen is 100 ppm or less, preferably 50 ppm or less.

The form of the reaction vessel is not particularly limited. A reactionvessel which can be generally used for an ammonia synthesis reaction canbe used. Examples of specific reaction forms include batch reactiontype, closed circulation reaction type, flow reaction type and the like.From the viewpoint of practical use, the flow reaction type ispreferable. Any one of a method using one type of reactor packed with acatalyst, a method using a plurality of reactors connecting each other,and a method using a reactor having a plurality of reaction layers inthe same reactor may be used.

The ammonia synthesis reaction from hydrogen and nitrogen mixed gas is avolumetric shrinkage type exothermic reaction. Therefore, in order toraise the ammonia yield, it is possible to use a reaction apparatus usedindustrially for removing reaction heat. Specifically, for example, amethod in which a plurality of reactors filled with catalysts areconnected in series and intercoolers are installed at the outlet of eachreactor in order to remove heat, or the like may be used.

In the method for manufacturing ammonia of the present invention, theammonia synthesis catalyst obtained by the production method of thepresent invention may be used alone, or used in combination with otherknown catalysts usually usable for ammonia synthesis.

EXAMPLE

Hereinafter, the present invention will be described in more detailbased on examples.

(BET Specific Surface Area Analysis)

In the following Examples and Comparative Examples, the measurement ofthe BET specific surface area was carried out by adsorbing nitrogen gasat the liquid nitrogen temperature on the surface of the object andmeasuring the amount of nitrogen mono-molecularly adsorbed. The analysisconditions are as follows.

[Measurement Condition]

Apparatus: BELSORP-mini II manufactured by Microtrac Bell Inc.

Adsorbed gas: nitrogen 99.99995 vol. %

Adsorption temperature: Liquid nitrogen temperature −196° C.

(Measurement of Ru Average Particle Diameter)

Measurement of the average particle size of Ru includes a chemicaladsorption method using CO and a direct observation method using anelectron microscope. The average particle diameter of Ru in the presentinvention is usually determined by a chemical adsorption method. Ifmeasurement by adsorption method is difficult, it is obtained by thedirect observation method.

<Chemical Adsorption Method>

The number of metal atoms exposed on the surface is estimated from theadsorbed amount of CO adsorbed, and the metal surface area (Am) per massof the supported metal is obtained. The metal surface area isrepresented by the following general formula (1).

Between the metal surface area (Am) and the average particle diameter(d) of the supported metal nanoparticles, the relationship expressed bythe following general formula (1) holds. Therefore, an average particlediameter of the supported Ru can be obtained from the metal surface area(Am) based on the general formula (2).Am=(V _(chem)×(SF/22414)×6.02×10²³×σ_(m)×10⁻¹⁸)/c  (1)

V_(chem):CO adsorption amount (cm³)

SF (stoichiometric factor): CO/Ru=1

σ_(m): metal cross-sectional area of one atom (nm²)

c: mass of metal-supported on sample (g)Am=4π(d/2)²×(α/c)  (2)

d: average particle diameter of metal nanoparticles (m)

α: number of metal particles

c: mass of metal-supported on sample (g)

[Measurement Condition]

Apparatus: BELCAT-A manufactured by Microtrac Bell Co.

Adsorbed gas: CO/He mixed gas CO concentration 9.5 vol. %

Adsorption temperature: 50° C.

In measurement by the chemical adsorption method, the measurement sampleis measured after performing the following pretreatment.

<<Sample Pretreatment Condition>>

The measurement sample was heated for 20 minutes from a room temperatureto 400° C. under a He gas flow and then kept at 400° C. for 30 minutesunder a hydrogen gas flow and then left at 400° C. for 15 minutes undera He gas flow and then cooled until 50° C.

<Direct Observation Method>

Metal nanoparticles were observed with an electron microscope such asTEM. Sizes of one hundred or more metal nanoparticles were measured, andthen an average value is obtained.

[Measurement Condition]

Apparatus: JEOL-ARM 200 F manufactured by JASCO Corporation

Acceleration voltage: 200 kV

(Activation Energy Measurement)

Activation Energy is an energy required to excite the starting materialof the reaction from the ground state to the transition state. If theenergy is lower, it shows that the reaction is easy. Activation Energycan be obtained by measuring temperature dependence of the reaction rateand calculating the slope when plotting the natural log of reaction rateagainst the reciprocal of the temperature.

Evaluation of the ammonia synthesis catalyst of the present inventionwas carried out by evaluating ammonia synthesis activity based on theammonia synthesis rate which was calculated by using the amount of NH₃produced using the ammonia synthesis catalyst of the present invention.The amount of NH₃ was measured by dissolving NH₃ produced in an aqueoussolution of sulfuric acid and determining the dissolved solution by anion chromatography.

(Ion Chromatographic Analysis)

The amounts of ammonia produced in the following Examples andComparative Examples were determined by dissolving the produced ammoniagas in a 0.05 M sulfuric acid aqueous solution and determining thedissolved solution by an ion chromatographic analysis using an absolutecalibration curve method.

[Measurement Condition]

Apparatus: HPLC Prominence manufactured by Shimadzu Corporation

Column: Shim-pack IC-C4 manufactured by Shimadzu Corporation

Length: 150 mm, inner diameter 4.6 mm

Eluent: A mixed aqueous solution of oxalic acid (3 mM), 18-crown-6-ether(2.0 mM)

Column temperature: 40° C.

Flow rate: 1.0 mL/min

Example 1

<Synthesis of Mayenite-Type Compound>

Ca(OH)₂ and Al(OH)₃ were weighed and mixed to obtain a mixed powder sothat the molar ratio of Ca atom to Al atom is Ca:Al=12:14. Distilledwater was added to the mixed powder so that the amount of the mixedpowder was 10 mass %. And a mixed solution having a total mass of 160 gwas obtained. Thereafter, this mixed solution was stirred and mixed in aplanetary ball mill at room temperature for 4 hours. The obtained mixedsolution was placed in a pressure-resistant closed vessel whilestirring, and was heated (hydrothermal treatment) at 150° C. for 6hours.

About 20 g of a precursor powder of mayenite-type compound: Ca₃Al₂(OH)₁₂was obtained by filtering off, drying and pulverizing the precipitateobtained in the hydrothermal treatment. A powder of mayenite-typecompound (hereinafter referred to as HT-C12A7) was obtained by heatingand dehydrating the precursor powder in the air at 600° C. for 5 hours.The obtained mayenite-type compound is a compound having a largespecific surface area. The specific surface area of the mayenite-typecompound is 50 to 60 m²/g.

<Supporting Ruthenium Compound on Mayenite-Type Compound>

1 g of the HT-C12A7 powder synthesized according to the above method,and 0.042 g of Ru₃(CO)₁₂ were placed in a Pyrex (registered trademark)glass tube and vacuum-sealed.

HT-C12A7 powder supporting 2 mass % of Ru (hereinafter referred to asRu/HT-C12A7) was obtained by rotating the vacuum-sealed glass tube in anelectric furnace and heating the glass tube according to the followingtemperature program.

[Temperature Program]

(1) Temperature was raised from room temperature to 40° C. for 20minutes, and then maintained at 40° C. for 60 minutes;

(2) After (1), after the temperature was raised from 40° C. to 70° C.for 120 minutes, and then maintained at 70° C. for 60 minutes;

(3) After (2), after the temperature was raised from 70° C. to 120° C.for 120 minutes, and then maintained at 120° C. for 60 minutes;

(4) After (3), after the temperature was raised from 120° C. to 250° C.for 150 minutes and then maintained at 250° C. for 120 minutes.

<Reduction Process and Subsequent Ammonia Synthesis Reaction>

A reaction of producing ammonia gas (NH₃) was carried out by reactingnitrogen gas (N₂) and hydrogen gas (H₂).

0.1 g of Ru/HT-C12A7, as a catalyst, obtained in above step was packedin a quartz glass tube and placed to a fixed-bed flow reactor to conducta reaction. Reaction was carried out under a condition that a flow rateof the gas was set to N₂: 15 mL/min, H₂: 45 mL/min and a total of 60mL/min; a reaction pressure was set to atmospheric pressure; and areaction temperature was set to 400° C. The gas from the above reactorwas bubbled through a 0.005 M sulfuric acid aqueous solution, and thegenerated ammonia was dissolved in the solution. The yielded ammoniumion was quantified by ion chromatography. The results are shown in Table1 and FIG. 1.

As shown in FIG. 1, the catalyst activity greatly improved with thereaction time.

As shown in Table 1, the initial synthesis rate of ammonia at 400° C.was 1.2 mmol/g·h. The ammonia synthesis rate was 2.9 mmol/g·h afterabout 24 hours reaction.

The average particle diameter of Ru determined by the chemicaladsorption method described above was 7.2 nm before the reaction and 9.0nm after the reaction. By the reduction process, the average particlediameter of Ru grew larger. After that, although the reaction time wasprolonged, no decrease in catalytic activity was observed.

Example 2

5 mass % Ru/HT-C12A7 was prepared in the same manner as in Example 1except that the amount of Ru supported was 5 mass % was used. Theobtained material was used as an ammonia synthesis catalyst reactionunder the same conditions as in Example 1. Ammonia was synthesized underthe same conditions as in Example 1. The results are shown in Table 1and FIG. 1.

As shown in FIG. 1, a catalyst activity was greatly improved with thereaction time.

Also, as shown in Table 1, an initial synthesis rate of ammonia at 400°C. was 2.1 mmol/g·h, and the ammonia formation rate after about 24 hoursreaction was 3.6 mmol/g·h.

The average particle diameter of Ru determined by the chemicaladsorption method described above was 8.9 nm before the reaction and was12.6 nm after the reaction. By the reduction process, the averageparticle diameter of Ru grew larger.

After that, although the reaction time was prolonged, no decrease incatalytic activity was observed.

Example 3

10 mass % Ru/HT-C12A7 was prepared in the same manner as in Example 1except that the amount of Ru supported was 10 mass % was used. Theobtained material was used as an ammonia synthesis catalyst reactionunder the same conditions as in Example 1. Ammonia was synthesized underthe same conditions as in Example 1. The results are shown in Table 1and FIG. 1.

As shown in FIG. 1, a catalyst activity was greatly improved with thereaction time.

Also, as shown in Table 1, an initial synthesis rate of ammonia at 400°C. was 2.1 mmol/g·h, and the ammonia formation rate after about 24 hoursreaction was 3.9 mmol/g·h.

The average particle diameter of Ru determined by the chemicaladsorption method described above was 10.7 nm before the reaction andwas 14.0 nm after the reaction. By the reduction process, the averageparticle diameter of Ru grew larger.

After that, although the reaction time was prolonged, no decrease incatalytic activity was observed.

Example 3A

<Pressure Dependence of Ammonia Synthesis Reaction>

The pressure dependence of ammonia synthesis reaction was investigatedby observing a change in catalytic activity by increasing the reactionpressure when the catalyst used in Example 3 was used and the reactiontemperature (400° C.) was maintained constant. The reactions werecarried out in the same manner as in Example 3 except for the reactiontemperature and the reaction pressure. The results are shown in FIG. 2.The ammonia synthesis rate at each reaction pressure was obtained bycontinuing the reaction until the measured value of the activity becamestable, and using the measured values at the stable state. The time tothe above stable state was from 1 hour to 2 hours.

As shown in FIG. 2, the catalytic activity of the 10 mass % Ru/HT-C12A7catalyst was greatly improved as the reaction pressure increases. Theammonia synthesis rate under the condition of pressure of 0.9 MPa was 10mmol/g·h. The result shows that hydrogen poisoning did not occur as thesame as C12A7 electride supporting Ru.

Comparative Example 1

C12A7 powder was obtained by mixing CaCO₃ powder and Al₂O₃ powder sothat the ratio of Ca to Al is 12:7, and heating the mixed powder in analumina crucible at 1300° C. for 6 hours by a solid phase method. A 2mass % Ru-supported C12A7 catalyst was synthesized by supporting Ru onthe obtained C12A7 powder in the same manner as in Example 1. Thespecific surface area of the 2 mass % Ru/C12A7 catalyst was 1 m²/g.

The ammonia synthesis activity of the catalyst at 400° C. was 7.2×10⁻¹mmol/g·h. As the reaction time elapsed, a remarkable improvement incatalyst activity was not observed.

Comparative Example 2

5 mass % Fe/HT-C12A7 catalyst was prepared in the same manner as inExample 2 except that 5 mass % of Fe was supported instead of Ru. Anammonia synthesis reaction was carried out under the same conditions asin Example 1.

As shown in Table 2, the initial synthesis rate of ammonia at 400° C.was 1.6×10⁻¹ mmol/g·h. The ammonia formation rate after the reaction for24 hours was 1.5×10⁻¹ mmol/g·h. When Fe was supported as a catalyst,unlike in the case of Ru, no improvement in catalytic activity wasobserved.

Comparative Example 3

5 mass % Co/HT-C12A7 catalyst was prepared in the same manner as inExample 2 except that 5 mass % of Co was supported instead of Ru. Anammonia synthesis reaction was carried out under the same conditions asin Example 1.

As shown in Table 2, the initial synthesis rate of ammonia at 400° C.was 0 mmol/g·h. The ammonia formation rate after the reaction for 24hours was 0 mmol/g·h. When Co was supported as a catalyst, unlike in thecase of Ru, no improvement in catalytic activity was observed.

Example 4

<Supporting Ru on Mayenite-Type Compound>

RuCl₃ was impregnated and supported on the surface of HT-C12A7 byweighing 1.0 g of the above-mentioned HT-C12A7, which was synthesized inthe same manner as in Example 1, and 0.05 g of RuCl₃.xH₂O (manufacturedby Aldrich, 99.9%) so that an amount of Ru supported was 2 mass %,adding the mixture to ethanol (manufactured by Kanto Chemical Co., Ltd.,99.5%), stirring it, and then removing the solvent under reducedpressure at 40° C. using a rotary evaporator. Since the supported Ruexisted as a form of RuCl₃ rather than metal Ru after supporting RuCl₃,it is impossible to measure a particle diameter. Therefore, apreliminary hydrogen reduction process was carried out at 250° C. inorder to measure the Ru particle diameter. As a result, 2 mass %Ru-loaded HT-C12A7 was obtained by performing the reduction process for6 hours at 250° C. using 20 volume % hydrogen gas/nitrogen gas.

At this time, the average particle diameter of Ru was measured by TEMand found to be 1.8 nm.

An Ammonia synthesis reaction was carried out under the same conditionsas in Example 1 using 2 mass % Ru-loaded HT-C12A7. As shown in FIG. 3,the catalyst activity was greatly improved with the reaction time. Asshown in Table 1, the ammonia synthesis rate at the second hour at 400°C. was 1.4×10⁻¹ mmol/g·h. The ammonia formation rate after 50 hoursreaction, was 2.8 mmol/g·h. After that, the temperature was lowered to320° C. and the ammonia synthesis activity was investigated, and it was4.0×10⁻¹ mmol/g·h. An activation energy Ea was 57 kJ/mol. The ammoniasynthesis rate at 300° C., which was estimated from the activationenergy, was 3.0×10⁻¹ mmol/g·h.

At this time, the average particle diameter of Ru grew to 2.2 nm afterthe reaction and the average particle diameter grew larger.

After that, although the reaction time was prolonged, no decrease in thecatalytic activity was observed.

Comparative Example 4

By using the same catalyst as in Example 4, an ammonia synthesisreaction was carried out in the same manner as in Example 4 except thatthe reaction temperature of ammonia formation reaction was 300° C. Asshown in FIG. 3, the ammonia synthesis rate at the second hour at 300°C. was 1.3×10⁻² mmol/g·h. The ammonia formation rate after 50 hoursreaction was 3.5×10⁻² mmol/g·h. Almost no increase in activity wasobserved.

At this time, the average particle diameter of Ru was 1.9 nm after thereaction.

Comparative Example 5

2 mass % Ru-supported HT-C12A7 catalyst was prepared in the same manneras in Example 4, except that the pretreatment of the catalyst before thereaction was heated at 400° C. for 6 hours in an oxygen atmosphere. Anammonia synthesis reaction was carried out under the same conditions asin Example 1.

The initial formation rate of ammonia at 400° C. was 5.2×10⁻¹ mmol/g·h.The catalyst activity was improved with the reaction time, and theammonia synthesis rate after about 24 hours the reaction was 2.0mmol/g·h. After that, the reaction time was prolonged, however, nofurther improvement in catalytic activity was observed.

TABLE 1 NH₃ synthesis rate (mmol/g · h) After Ru particle SupportedInitial reaction diameter (nm) Catalyst amount Catalytic (processing(reaction After reaction Metal (mass %) Support time) time) Initial(reaction time) Example 1 Ru 2 HT-C12A7 1.2 2.9 7.2  9.0 (1 hr) (24 hr)(24 hr) Example 2 Ru 5 HT-C12A7 2.1 3.6 8.9 12.6 (1 hr) (24 hr) (24 hr)Example 3 Ru 10 HT-C12A7 2.1 3.9 10.7 14.0 (1 hr) (24 hr) (24 hr)Example 4 Ru 2 HT-C12A7 1.4 × 10⁻¹ 2.8 1.8  2.2 (2 hr) (50 hr) (50 hr)Comparative Ru 2 Solid-phase 7.2 × 10⁻¹ 7.2 × 34.9 34.9 Example 1method-C12 (1 hr) 10⁻¹ (24 hr) A7 (24 hr)

TABLE 2 NH₃ Synthesis Rate (mmol/g · h) After Cat- Supported Initialreaction alyst amount Catalytic (processing (reaction metal (mass %)Support time) time) Example 2 Ru 5 HT-C12A7 2.1 3.6 (1 hr) (24 hr)Comparative Fe 5 HT-C12A7 1.6 × 10⁻¹ 1.5 × 10⁻¹ Example 2 (1 hr) (24 hr)Comparative Co 5 HT-C12A7 0   0   Example 3 (1 hr) (24 hr)

Example 5

A mayenite-type compound was synthesized except that the Ca(OH)₂,Al(OH)₂, and Ba(OH)₂ were weighed and mixed so as to haveCa:Al:Ba=11.75:14:0.25. Further, in the same manner as in Example 1, Ruwas supported and ammonia synthesis was carried out.

As shown in FIG. 4, the catalyst activity greatly improved with thereaction time, and the ammonia synthesis rate after about 20 hoursreaction was 5.1 mmol/g·h. The average particle diameter of Rudetermined by the CO adsorption method was 9.6 nm before the reaction,and after the reaction, the average particle diameter of Ru grew largerto 13.7 nm.

After that, although the reaction time was prolonged, no decrease incatalytic activity was observed.

As shown in Examples 1 to 5, the HT-C12A7 supporting Ru has a greatlyimproved catalytic activity during the ammonia synthesis reaction andshows an ammonia synthesis rate comparable to the Ru/C12A7 electride.FIG. 1 shows the relationship between Examples 1 to 3 and ComparativeExample 2, and 2 mass % Ru— supported C12A7 electride (obtainedaccording to the description of Comparative Example 3 in WO2014/034473).Then, before and after the ammonia synthesis reaction, growth of Ruparticles of the used catalyst was observed. Therefore, it is expectedthat Ru particles were strongly immobilized on the support C12A7 whilegrowing Ru particles during the reaction. At this time, O²⁻ ions nearinterface between Ru nanoparticles and the C12A7 cages were released bythe catalytic action of Ru. As a result, it is considered that electronswere formed in the cage and the catalytic activity was greatly improved.In fact, the Ru/HT-C12A7 catalyst with improved activity showed about0.5 order for N₂ and about 0.9 order for H₂. In the Ru/C12A7 catalystwhich did not contain electrons and was synthesized by the solid phasemethod of Comparative Example 4, the order of reaction is about 1.0order for N₂ and 0 order for H₂. For Ru/C12A7 electride, the order ofreaction is about 0.5 order for N₂ and 1.0 order for H₂. These resultsrevealed that the Ru/HT-C12A7 catalyst has ammonia synthesizing activitywith almost the same mechanism as that of Ru/C12A7 electride.

In addition, when the catalyst in which RuCl₃.xH₂O as a Ru source wassupported on HT-C12A7 was used, the same phenomenon occurred as the casewhere Ru₃(CO)₁₂ was used as the Ru source. The catalyst activity may begreatly improved during the reaction.

Example 6

<Synthesis of Ru/HT-C12A7 in which Ba was Added>

35.5 mg of barium diethoxide (Ba(OC₂H₅)₂: manufactured by Wako PureChemical Industries, purity 99.5%) was dissolved in 45 mL of ethanol andstirred for about 20 minutes. Next, 11.3 mg of water and 5 mL of ethanolwere added to the solution, and the mixture was further stirred forabout 15 minutes to prepare a mixed solution. 0.3 g of Ru/HT-C12A7described in Example 2 was added to the obtained mixed solution, and themixture was stirred for about 20 minutes. Ru/HT-C12A7 powder (Ru:Ba=1:1(molar ratio)) in which Ba was added (hereinafter referred to asBa-Ru/HT-C12A7) was obtained by removing the solvent from the mixedsolution using a rotary evaporator and drying the product.

The metal-supported material, Ba-Ru/HT-C12A7 was as a catalyst. Thecatalyst was contacted with a mixed gas of nitrogen and hydrogen, and anammonia synthesis reaction was carried out. The ammonia synthesisreaction was carried out in the same manner as in Example 1 except thatthe reaction temperature was 340° C. The results are shown in Table 3.

As shown in Table 3, the ammonia synthesis rate after 30 hours reactionat 340° C. was 4.7 mmol/g·h. The initial synthesis rate of ammonia at400° C. was 4.4 mmol/g·h, and the ammonia synthesis rate after 30 hoursreaction at 400° C. was 6.9 mmol/g·h.

The average particle diameter of Ru obtained by the direct observationmethod of TEM was 1.6 nm before the reaction and was 2.2 nm after thereaction. The average particle diameter of Ru grew greatly by thereduction process.

After that, although the reaction time was prolonged, no decrease incatalytic activity was observed.

Example 7

Ba(C₅H₇O₂)₂.xH₂O (Aldrich purity: 98%) 47.6 mg was dissolved in 100 mLof ethanol and was stirred for about 20 minutes. Ru/HT-C12A7 powder inwhich Ba was added (Ru:Ba=1:1 (molar ratio)) was prepared in the samemanner as in Example 6 except that Ru/HT-C12A7 0.3 g was added to thissolution.

Ammonia synthesis reaction was carried out under the same conditions asin Example 6, except that the metal-supported material was used as acatalyst, and the results are shown in Table 3.

As shown in Table 3, the ammonia formation rate after 30 hours reactionat 340° C. was 3.1 mmol/g·h. The initial production rate of ammonia at400° C. was 4.3 mmol/g·h, and the ammonia formation rate after 30 hoursreaction at 400° C. was 6.8 mmol/g·h.

The average particle diameter of Ru was the same as in Example 6, andthe average particle diameter of Ru grew greatly due to the reductionprocess.

After that, although the reaction time was prolonged, no decrease incatalytic activity was observed.

Example 8

Ba-Ru/HT-C12A7 powder was obtained in the same manner as in Example 7except that tetrahydrofuran (THF) was used in place of ethanol among thematerials used in Example 7.

Ammonia synthesis reaction was carried out under the same conditions asin Example 6 except that the Ba-Ru/HT-C12A7 was used as a catalyst, andthe results are shown in Table 3.

As shown in Table 3, the ammonia formation rate after 30 hours reactionat 340° C. was 2.7 mmol/g·h. The initial production rate of ammonia at400° C. was 4.0 mmol/g·h, and the ammonia formation rate after 30 hoursreaction at 400° C. was 5.9 mmol/g·h.

The average particle diameter of Ru was the same as in Example 6, andthe average particle diameter of Ru grew greatly due to the reductionprocess.

After that, although the reaction time was prolonged, no decrease incatalytic activity was observed.

Example 9

Ba-Ru/HT-C12A7 powder (Ru:Ba=1:2 (molar ratio)) was obtained in the samemanner as in Example 6 except that 271.1 mg of Ba(OC₂H₅)₂ and 22.5 mg ofwater were used.

Ammonia synthesis reaction was carried out under the same conditions asin Example 6 except that the Ba-Ru/HT-C12A7 was used as a catalyst, andthe results are shown in Table 3.

As shown in Table 3, the ammonia formation rate after 30 hours reactionat 340° C. was 3.8 mmol/g·h. The initial production rate of ammonia at400° C. was 3.7 mmol/g·h, and the ammonia formation rate after 30 hoursreaction at 400° C. was 6.3 mmol/g·h.

The average particle diameter of Ru was the same as in Example 6, andthe average particle diameter of Ru grew greatly due to the reductionprocess.

After that, although the reaction time was prolonged, no decrease incatalytic activity was observed.

Example 10

Ammonia synthesis reaction was carried out under the same conditions asin Example 6, except that Ru/HT-C12A7 described in Example 2 was used asa catalyst, and the results are shown in Table 3.

As shown in Table 3, the ammonia formation rate after 30 hours reactionat 340° C. was 2.3 mmol/g·h. The initial production rate of ammonia at400° C. was 3.7 mmol/g·h, and the ammonia formation rate after 30 hoursreaction at 400° C. was 4.3 mmol/g·h.

TABLE 3 NH₃ Synthesis Rate (mmol/g · h) 340° C. 400° C. 400° C. After 30hr reaction Initial After 30 hr reaction Example 6 4.7 4.4 6.9 Example 73.1 4.3 6.8 Example 8 2.7 4.0 5.9 Example 9 3.8 3.7 6.3 Example 10 2.33.7 4.3

FIG. 5 shows the time change of ammonia synthesis when themetal-supported material described in Example 6 was used as an ammoniasynthesis catalyst. The reaction conditions were shown as follows: thereaction temperature was 400° C. and the reaction pressure wasatmospheric pressure (0.1 MPa). From FIG. 5, it can be seen that thecatalyst activity was improved with the reaction time and the catalyticactivity was improved to nearly equilibrium conversion. Similarly, themetal-supported materials described in the other examples (Examples 7 to10) in which Ba was added had improved catalytic activities to a valueclose to the equilibrium conversion. As a result, performance comparisonof each catalyst could not be made at 400° C. Therefore, the reactiontemperature was lowered to 340° C. and comparison was made.

Example 11

<Pressure Dependence of Ammonia Synthesis Reaction>

The same catalyst as used in Example 6 was used and the reactiontemperature (400° C.) was maintained to constant. The pressuredependence of the ammonia synthesis reaction was investigated byobserving change in catalytic activity when the reaction pressure wasincreased. The results are shown in FIG. 6.

FIG. 6 is a graph showing change in catalytic activity when the reactionpressure was increased by keeping the reaction temperature (400° C.)constant when the metal-supported material described in Example 6 wasused as an ammonia synthesis catalyst. The results were measured in thesame manner as in Example 3A.

As shown in FIG. 6, it was found that the catalyst activity of Example 6was greatly improved with increasing reaction pressure. The ammoniasynthesis rate under the condition pressure of 0.9 MPa was 28 mmol/g·h.This result shows that it is not subjected to hydrogen poisoning as thesame as the Ru-supported C12A7 electride.

Example 12

<Temperature Dependence of Ammonia Synthesis Reaction>

The same catalyst as used in Example 6 was used, and the reactionpressure (0.9 MPa) was kept constant.

The temperature dependence of the ammonia synthesis reaction was studiedby observing changes in catalytic activity when the reaction temperaturewas raised. The results are shown in FIG. 7

As shown in FIG. 7, when Ba-Ru/HT-C12A7, which is a metal-supportedmaterial obtained in Example 6, was used as an ammonia synthesiscatalyst, as the reaction temperature increased, the catalytic activitygreatly improved. As compared with Ru/HT-C12A7 in which no Ba was added,which was obtained in Example 2, a much higher ammonia synthesisactivity was shown within whole temperature range from 280° C. to 400°C. In particular, in the low temperature region of 340° C. or lower, itshowed a catalytic activity about 5 times higher than that ofRu/HT-C12A7 in which no Ba was added.

The method for manufacturing an ammonia synthesis catalyst of thepresent invention is a simple manufacturing method and can produce acatalyst having a high ammonia synthesizing activity. This catalyst madeit possible to synthesize ammonia at a low pressure compared with theHaber-Bosch method. Furthermore, an ammonia synthesis can be carried outmore conveniently.

The invention claimed is:
 1. A method for manufacturing an ammoniasynthesis catalyst, the method comprising: a first step of preparing12CaO.7Al₂O₃ having a specific surface area of 5 m²/g or more; a secondstep of supporting a ruthenium compound on the 12CaO.7Al₂O₃; and a thirdstep of performing reduction process on the 12CaO.7Al₂O₃ on which theruthenium compound is supported (hereinafter referred to asruthenium-supported C12A7) obtained in the second step, wherein thereduction process is carried out until an average particle diameter of aruthenium after the reduction process increases by 15% or more withrespect to an average particle diameter of a ruthenium before thereduction process.
 2. The method for manufacturing an ammonia synthesiscatalyst according to claim 1, wherein a specific surface area of theruthenium-supported C12A7 after the reduction process step is 5 m²/g ormore.
 3. The method for manufacturing an ammonia synthesis catalystaccording to claim 1, wherein in the first step, preparing 12CaO.7Al₂O₃is carried out by a hydrothermal synthesis method, a sol-gel method, acombustion synthesis method or a co-precipitation method.
 4. The methodfor manufacturing an ammonia synthesis catalyst according to claim 1,wherein in the second step, supporting the ruthenium compound is carriedout by an impregnation method or a vapor deposition method.
 5. Themethod for manufacturing an ammonia synthesis catalyst according toclaim 1, wherein in the step of performing reduction process, thereduction process is carried out by using a gas containing hydrogen. 6.The method for manufacturing an ammonia synthesis catalyst according toclaim 1, the method further comprises, following the first step, a stepof molding the 12CaO.7Al₂O₃ obtained in the first step.
 7. The methodfor manufacturing an ammonia synthesis catalyst according to claim 1,the method further comprises, following the second step, a step ofmolding the ruthenium-supported C12A7 obtained in the second step. 8.The method for manufacturing an ammonia synthesis catalyst according toclaim 1, wherein the ammonia synthesis catalyst comprises at least analkali metal atom or an alkaline earth metal atom.
 9. A method formanufacturing ammonia, comprising: a first step of preparing12CaO.7Al₂O₃ having a specific surface area of 5 m²/g or more; a secondstep of supporting a ruthenium compound on the 12CaO.7Al₂O₃; a thirdstep of performing reduction process on the 12CaO.7Al₂O₃ on which aruthenium compound is supported (hereinafter referred to asruthenium-supported C12A7) obtained in the second step, wherein thereduction process is carried out until an average particle diameter of aruthenium after the reduction process increases by 15% or more withrespect to an average particle diameter of a ruthenium before thereduction process; and a step of producing ammonia by contacting a gascontaining nitrogen and hydrogen with an ammonia synthesis catalystwhich is obtained by the reduction process in the third step.
 10. Themethod according to claim 9, wherein in the step of performing reductionprocess, the reduction process is performed by using a gas containinghydrogen.
 11. The method according to claim 9, wherein in the step ofperforming reduction process, the reduction process is performed with agas containing hydrogen and nitrogen.
 12. The method according to claim9, wherein the ammonia synthesis catalyst comprises at least an alkalimetal atom or an alkaline earth metal atom.
 13. The method formanufacturing an ammonia synthesis catalyst according to claim 1,wherein the reduction process is carried out at atmospheric pressure,and the time of the reduction process is 20 hours or more, or thereaction pressure is carried out at 1 MPa or more, and the time of thereduction process is 5 hours or more.